forbidden-fruit factor
This is the thing that makes any one of your girlfriend/boyfriend's good friends and best friends 10x more attractive than they've ever been before because of the fact that you can never have them.
This makes people you'd normally not be attracted to seem even hot at times.

Single guy: Dude, Becky and Sierra are like 5's.
Taken guy: It's the FFF man; they're at least 8's in my eyes now.

Female-Female-Female, an all girl threesome. Can involve all three at once in a daisy chain or just general fondling and kissing. Or two could be going at it while the other is watching and pleasuring herself, and then switch round. One could be the focus of attention where the second sits on her face and the third eats her out.

It's all...rather...nice...

Use your imagination...;)

Back in January, I was in a FFF and I can't stop thinking about it, so much energy, so hot...

More specifically, someone who is in touch with their emotions and graceful - sympathetic and empathetic, artistic and delicate - feels pain, and has emotional and intellectual baggage making them complex and at times irrational. This causes them to appear out of touch and uncaring, yet desirable.

FFF; Not run of the mill, abnormal, strange or unique. Guys you hate, but can't avoid loving.